Mitochondrial Fission in Huntington's Disease

描述（由申请人提供）：亨廷顿病（HD）是一种遗传性神经退行性疾病，由亨廷顿蛋白（htt）中的异常多聚谷氨酰胺（polyQ）扩增引起，导致进行性痴呆、运动缺陷和精神异常。目前，HD仍然无法治愈。在HD中，纹状体和皮质神经元通过未知机制选择性死亡。我们迫切需要科学上的突破来揭示htt突变体是如何导致神经元死亡的。新的证据表明，线粒体功能障碍在HD的发病机制中起着核心作用。但是，线粒体在HD中究竟是如何受损的仍不清楚。线粒体是一种动态的细胞器，能够迁移、分裂和融合。线粒体的分裂和融合是由动力蛋白相关的GTP酶与竞争活动编排的。在正常情况下，线粒体在神经元中形成索状细丝，允许有效的能量传输，代谢物的混合，Ca2+缓冲和mtDNA突变的沉默。在这里，我们将测试新的假设是否持续的线粒体分裂代表一个机制的基础上线粒体功能障碍牵连HD发病机制。我们将解决以下问题：（1）突变htt触发连续线粒体分裂，这反过来又导致线粒体超微结构损伤，能量不足，线粒体呼吸功能受损，ROS产生，异常Ca 2+稳态，和mtDNA丢失？(2)突变体htt是否招募并激活线粒体裂变机制？(3)线粒体分裂是否在突变型htt诱导的神经变性和细胞死亡中起因果作用？为了回答这些问题，我们将分离初级纹状体或皮质神经元。此外，我们将采用突变htt转基因小鼠和死后HD脑组织。我们将使用跨学科和先进的技术来分析它们，包括3D时间推移成像，EM断层扫描，分子遗传学，药理学，生物化学和生物能量学。我们还将开发新的算法，通过3D延时成像来量化线粒体分裂和线粒体聚集体的形成。这项研究将提高我们对突变htt如何触发神经元死亡的基本理解。这里获得的结果可能提供了一个新的机制基础的代谢和线粒体缺陷的基础HD和其他polyQ疾病。最重要的是，这项研究可能为有效治疗HD中进行性神经元丢失带来新的希望，因此患者可以改善生活。

DESCRIPTION (provided by applicant): Huntington's disease (HD) is a hereditary neurodegenerative disorder and is caused by an abnormal polyglutamine (polyQ) expansion in the huntingtin (htt) protein, leading to progressive dementia, motor defects and psychiatric abnormalities. Presently, HD remains without cure. In HD striatal and cortical neurons die selectively by an unknown mechanism. Scientific breakthroughs are desperately needed to unravel how mutant htt causes neuronal demise. New evidence emerged indicating that mitochondrial dysfunction plays a central role in the pathogenesis underlying HD. But, exactly how mitochondria become injured in HD remains unclear. Mitochondria are dynamic organelles able to migrate, divide (undergo fission) and to fuse. Mitochondrial fission and fusion is choreographed by dynamin-related GTPases with competing activities. At normal conditions mitochondria form cable-like filaments in neurons, allowing efficient energy transmission, mixing of metabolites, Ca2+ buffering, and silencing of mtDNA mutations. Here, we will test the novel hypothesis whether persistent mitochondrial fission represents a mechanistic basis for the mitochondrial dysfunction implicated in HD pathogenesis. We will address the following questions: (1) Does mutant htt trigger continuous mitochondrial fission, which in turn results in ultrastructural damage of mitochondria, energy deficits, impaired mitochondrial respiration, ROS production, abnormal Ca2+ homeostasis, and mtDNA loss? (2) Does mutant htt recruit and activate the mitochondrial fission machinery? (3) Does mitochondrial fission play a causal role in mutant htt-induced neurodegeneration and cell death? To answer these questions we will isolate primary striatal or cortical neurons. Additionally, we will employ mutant htt transgenic mice and postmortem HD brain tissue. We will analyze them using interdisciplinary and advanced techniques including 3D timelapse imaging, EM tomography, molecular genetics, pharmacology, biochemistry, and bioenergetics. We will also develop new algorithms to quantify mitochondrial fission and mthtt aggregate formation by 3D time-lapse imaging. This study will improve our basic understanding of how mutant htt triggers neuronal demise. Results obtained here may offer a new mechanistic basis for the metabolic and mitochondrial defects underlying HD and perhaps other polyQ disease. Most importantly, this study may bring new hopes for effective treatments to conquer progressive neuron loss in HD, so patients can lead improved lives.